It has been observed in this laboratory that live virulent mycobacteria are toxic for normal rabbit alveolar macrophages. In contrast, if virulent mycobacteria are killed by mild methods (65 degrees-30 min) this toxicity is lost. The proposed project will involve various experimental approaches to elucidate the nature of this toxicity. Avirulent and virulent strains of mycobacteria will be phagocytized in vitro and in vivo by normal or "immune" rabbit alveolar macrophages. The post-phagocytic events will be followed by electron microscopy including monitoring DNA synthesis (autoradiography) by intracellular mycobacteria and the fusion pattern of primary and secondary lysosomes as well as the large electron dense granules commonly present in "granulomatous" macrophages. Secondary lysosomes will be labeled with ferritin and monitored for possible fusion with phagosomes. Other experimental approaches will involve the effect of virulent intracellular mycobacteria on in vitro migration of normal macrophages and PMNs, effect on hexose monophosphate shunt and on O2 consumption.